Photographic emulsion



Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE 2,222,262 PHOTOGRAPHIC EMULSION John A. Leermakers, Rochester, N Y., assignor to Eastman Kodak Company, Rochester, N. Y., a. corporation of New Jersey No Drawing. Application February 2, 1939, Serial N0. 254,253

Claims. (01. 95-7) .tion is substantially greater in some spectral region than is the sensitization produced by any one of the dyes in the absence of the other or others. The combined elfect is not additive. This phenomenon has been termed "supersensitization. Instances of supersensitizing combinations are described in United States Patents 2,075,046; 2,075,047 and 2,075,048, each dated March 30, 1937.

I have now found that unusual-'supersensitizin effects can be obtained in silver halide emulsions by employing a mixture or combination of a sensitizing dye with silver cyanide. Such emulsions possess not only highspeeds, but the other properties essential to a practical high speed emulsion, providing the concentration of the silver cyanide, with respect to the silver halide in the emulsion, lies within a certain range as hereinafter set forth. My new method of supersensitizing spectrally (optically) sensitized emulsions is an improvement over the aforesaid known methods, since even the effect obtained by a supersensitizing combination of two or more sensitizing dyes can be enhanced by my new method. I

I am aware the alkali cyanides have been proposed, as ingredients for self-toning photographic emulsions. Alkali cyanides, however, cannot be employed in practicing my invention, since they have a deleterious, rather than a beneficial eifect, on the sensitivity of the emulsions, probably owing to the solvent action of the alkali cyanides on the silver halides.

'It is, accordingly, an object of my invention to provide new photographic emulsions. A further object is to provide a process for preparing such emulsions. Other objects will appear hereinafter.

According to my invention, I incorporate silver cyanide in unwashed or washed, finished silver halide emulsions, together with a sensitizing dye.

My invention is particularly directed to washed,

finished emulsions; since it is not advantageous to employ some sensitizing dyes in unwashed emulsions; Furthermore, the efiects obtainable according to my invention are much more pronounced in washed, finished emulsions.

It is, of course, well known that silver halide emulsions can be prepared according to the following fundamental steps:

. eterious effect on the emulsion.

1. Precipitation, wherein the silver halide is pre- I cipitated by the interaction of a soluble silver salt and an excess of a soluble halide in the presence of a carrier, such as gelatin.

2. Digestion, wherein the above precipitate is digested for aperiod of time at a raised temperature, e. g. 50 to 60 C., with" or without the addition of further carrier.

3. Washing, wherein the ripened, solidified (e. g. by chilling) emulsion is washed with water to remove soluble salts.

4. Melting out and second digestion, wherein the washed emulsion is heated for a period of time, with or without the addition of further carrier, after which the emulsion is fiowable.

Of course, variations of the above four steps can be employed. An emulsion, which is coated without washing, I call an unwashed, finished emulsion. An emulsion, which is coated after washing and melting out, I call a, washed, finished emulsion.

The silver cyanide is advantageously incorporated in the emulsion in the form of a colloidal dispersiomi. e. dispersed in gelatin, gum arabic or other hydrophyllic colloid which is compatible with the emulsion and has substantially no del- However, the silver cyanide can be incorporated in the solid form, advantageously finely divided. The silver cyanide can be added to the'emulsion prior to, simultaneously with or after the addition of the sensitizing .dye. The amount of silver cyanide added should not be more than about three percent by moles of the silver halide in the emulsion. I have found that larger amounts, e. g.

5%, do not give rise to emulsions ofhigh speed and practical keeping qualities. From about one-half to abouttwo mole percent of silver cyanide is advantageously employed. Smaller amounts can be employed, although, of course, as

the concentration becomes very small, the bone ficial effects are quite small. Generally speaking,

the lowest practical concentration of silver cyanide is of the order of 0.05 mole per cent.

As sensitizing dyes, I employ; any of the known types and advantageously those which are not of a markedly acidic nature, i. e. those devoid of sulfonic acid (S0311), sulfinic acid (S0211), sulof dyes which aredevoid of the aforesaid aeidic groups and their metal or ammonium salt forms.

A number of sensitizing 'cyanine dyes are, of

course, well known substances; 'Sensitizin'g merocyanine dyes aredescribed, for example, in-

United States Patent 2,078,233, dated April 27,

, Serial No. 101,105, filed September 16, 1936.

The sensitizing dyes can be employed in various.

concentrations depending upon the effects desired. As is well known in the art, the sensitivity conferred upon an emulsion by a sensitizing dye does not increase proportionately to the concentration of the dye in the'emulsion, but rather passes through a maximum as the concentration is increased. The dyes can be employed in the optimum concentration. or in concentrations greater or less than the optimum. The optimum concentration of a sensitizing dye can be determined in a manner well known in'the art by measuring the sensitivity of a series of emulsions containing different concentrations of the sensitizing dye. Ordinarily, the optimum or near optimum concentration is of the order of to mg. of the dye per liter of the emulsion.

. The sensitizing dyes are advantageously added u to the emulsion in the form of their solutions in suitable solvents. Methyl alcohol suffices as a solvent for most sensitizing dyes. Acetone is frequently a satisfactory solvent for those dyes having a very' limited solubility in methyl alcohol. Both the sensitizing dyes and the silver cyanide should be thoroughly dispersed throughout the emulsion.

My invention is particularly directed to the ordinarily employed gelatino-silver-halide emulsions and more particularly to the gelatino-silver-halide emulsions in which the majority of the silver halide is silver bromide, such as the silver bromide and silver bromiodide emulsions customarily employed in the art. The effects obtained in bromide and bromiodide emulsions are considerably more pronounced than those obtained in emulsions containing large amounts of silver chloride; My invention can be employed with silver halide emulsions in which the carrier is other than gelatin, for example, a resinous substance or cellulosic derivative which has substantially no deleterious efiect on the light-sensitive materials in the emulsion.

The following example illustrates the manner of preparing my new emulsions. This example is not intended to limit myinvention.

Example A colloidal dispersion of silver cyanide in gelasion containing 0.1 g.

' thiocyanates.

tin was prepared as follows: two solutions, A and B were prepared in the following manner:

Solution A. -Prepared by dissolving 200 g. of silver nitrate in 1000 cc. of water. Solution B.-Prepared by dissolving 65 g. of sodium cyanide in 1000 cc. of water.

Solution A was poured into solution B at about 25 C. After the precipitate settled, it was washed four or five times. with water by decantation. To the washed precipitate were added 60 cc. of 28% ammonium hydroxide. Tothe resulting paste were added 60 g. of gelatin dissolved in 3000 cc. of water at 50.. C. The resulting mixture was stirred vigorously'ior an of this time, 200 g. of dry gelatin were dissolved in the mixture at 50 C. The resulting dispersion was cooled until it set. ,I It was then shredded and washed with water for one-half hour.

To a washed, finished, flowable gelatino-silverbromiodide emulsion, prepared by the ammonia process containing 10 g. of silver halides wasadded, with stirring, a quantity of the above disperof silver cyanide. To the resulting mixture were added, with stirring, 4 mg. of 2,2'-diethyl-8-methyl 3,4,3,4' dibenzothiacarbocyanine iodide dissolved in a small amount of methyl alcohol. sessed a green sensitivity about 100% greater than the same emulsion containing the same sensitizing dye in the same concentration, but lacking the silver cyanide.

Silver cyanide can be incorporated in the finished emulsions, as illustrated in the foregoing example, together with other substances, e. g. silver thiocyanate, ammonium thiocyanates, alkali metal thiocyanates or alkaline earth metal Silver thiocyanate is advantageously added to emulsions in the form of a colloidal dispersion in a hydrophyllic colloid, while the water-soluble thiocyanates can be added in the form of their aqueous solutions. See my copending application Ser. No. 254,252 filed of even date herewith.

Still further examples of the preparation of my new emulsions could be given, but the foregoing is believed to demonstrate adequately the manner of practicing my invention.

Photographic elements comprising my new emulsions can bemade up in the usual manner by coating the fiowable emulsions on to a support of asuitable material, such as glass, photographic paper, cellulose derivatives or resins for example, to desired thickness, and then drying the emulsion,

Illustrations of the effects that can be obtained according to my invention are'iound in the following table:

. Percent increase in speed sensitizing dye owing to AgCN AgON Concentration, Emulsion Concentramole percent tion, millioi silver halide Name grams per in emulsion Clear Blue Green Red liter of emulsion 1 Gelatino-silver bro- 2,2-diethyl-8-metliyl-3,4,3, 20 0.5 +100 +100 +100 miodide. 4 dibenzothiacarbocyan- 1 ine chloride. 2 Gelatino-silver bro- 2,2-diethyl-8-ethylthiacar- 20 1.0 +80 +25 miodide. bocyanine iodide. 3 Gelatino-silver bro 3-ethyl-5-[(2-ethyl-l(2)-ben- 10 0.5 +80 +80 +80 0 miodide. zoxazylidene) ethylidene'] rhodanine. 4 Gelatino-silver bro- 2-[4-(l-pi eridyl)-A -buta- 20 0.5 +100 +80 +80 0 miodide. dienyl -fl-naphthothiazole ethiodide.

1 As measured through a Wratten No. 47 filter. 1 As measured through a Wratten N o. 58 filter.

3 As measured through a Wratten No. 25 filter.

The resulting emulsion pos-" hour. At the end The considerable increase sin speed that can be attained according to my invention are apparent from the above table. Under (1) in the above table, an ordinary gelatino-silver-bromiodide emulsion sensitized with 2,2'-diethyl-3,4,3,4'-dibenzothiaearbocyanine chloride, owing to the silver cyanide, has increased in clear speed by about one hundred percent, in blue speed by about one hundred percent, in green speed by about one hundred percent and in red speed by about eighty percent.

I have obtained particularly useful emulsions from silver cyanide with ordinary gelatino-silver bromide and bromiodide emulsions sensitized with sensitizingdyes from the following group of dyes:

I. Carbocyanine dyes having the following general formula:

Q\ XTI/ wherein A represents hydrogen or a CilH2n+=1 7 group wherein n' represents a positive integer not greater than five, Q and Q represent oxygen or I sulfur, R and 'R' represents a ,CnH-mn group wherein n represents a positive integer not greater than flve,and X represents an acid radical, preferably halide.

111. Carbocyamnes of the following general formula:

wherein A represents hydrogen or a Cal-lam group wherein n represents a positive integer not greater than five, Q 'and Q represent'oxygen or sulfur, R and R represent a" CnH2n+1' gI0up "wherein n represents a positive integer not greater than fiveX represents an acid radical, preferably halide, and wherein the nucleus Z may under V above.

carry simple substltuents,-such as chlorine atoms or alkyl groups, for example.

IV; Hemidicarbocyanines of the following general formula:

wvherein Q represents oxygen, sulfur or selenium, R represents a CnH2n+l group wherein n represents a positive integer not greater than five, X represents an acid radical, preferably halide, and wherein the nucleus Z may carry simple substituents, such as chlorine atoms or alkyl groups, for example.

v. Hemidicarbocyanines of the following general formula:

wherein Q represents oxygen or sulfur, and R and X have the values set forth'above under IV.

VI. Hemidicarbocyanines of the following general formula:

wherein Q, R, Xand Z have the values set forthabove under IV.

VII. Hemidicarbocyanines of the following general formula: r

wherein Q, R and X have the values set forth VIII. Hemic'arboxonols of the, following gen eral formula:

wherein Z represents the non-metallic atoms necessary to complete a rhodanine nucleus, a 3- alkyl-2,4(3,5) -oxazoledione nucleus, a 2-thiohydantoin nucleus, a 2-diphenylamino-'-4(5) -thiazolone nucleus or a L-benzothiazyl-Zi-methyl 5-pyrazo lone nucleus.

IX. Hemicarboxonols of the following general formula:

wherein Z has the value given under VIl'Iabove.

X. Merocarbocyanines of the following generalformula:

wherein R represents 'a CnHZn-l-l group wherein n represents a positive integer not greater than five, Q represents oxygen, sulfur or selenium and Z has the values set forth under VIII above and the nucleus Y may carry simple substituents, such as chlorine atoms or alkyl groups.

I determine the sensitivity of emulsions in the usual manner, first coating the prepared emulsion on a glassplate to suitable thickness and drying the coated emulsion. The resulting photographic plateris thentested by means of a wedge spectrograph and a sensitometer, whereby spectral sensitivity and speed of the emulsion on the plate is determined.

What I claim as my invention and desire to be secured by Letters Patent of the United States is:

l. A photographic silver halide emulsion. containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introducedinto the finished emulsion in the form of the simple compound silver cyanide, in a concentration equal tonot more than about three percent by moles of the silver halide in the emulsion.

2. A photographic gelatino-silver-halide emulsion containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced into the finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to not more than about three percent by moles of the silver halide in the emulsion.

3. A photographic gelatino-silver-halide emulsion selected from the group consisting of gelatino-silver-bromide and gelatino-silver-bromiodide emulsion, containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced into the finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to not more than about three percent by moles of the silver halide in the emulsion.

4. A photographic gelatino-silver-halide emulsion selected from the group consisting of gelatino-silver-bromide and gelatino-silVer-bromiodide emulsions containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced into-the washed, finished emulsion in the form of the- 5. A photographic gelatino-silver-halide emulsion containing a sensitizing dye for the emulhemioxonol dyes which are devoid of sulfonic,

sulfinic, sulfuric acid, and carboxylic acid groups and the metal and ammonium salt forms of said acid groups, and containing silver cyanide, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to not more than about three percent by moles of the silver halide in the emulsion.

7. A photographic gelatino-silver-halide emulsion selected from the group consisting of gelatino-silver-bromide and gelatino-silver-bromiodide emulsions containing a sensitizing dye for the emulsion, said dye being selected from the group consisting of cyanine, merocyanine, hemicyanine and hemioxonol dyes which are devoid of sulfonic, sulfinic, sulfuric and carboxylic acid groups and the metal and ammonium salt forms of said acid groups, and containing silver cyanide, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to not more than about three percent by moles of the silver halide in the emul- SlOIl.

8. A photographic silver halide emulsion containing a sensitizing dye for theemulsion and containing silver cyanide-said silver cyanide having been introduced in the finished emulsion in the form of the simple compound silver cyanide. in a concentration equal to from about 0.05 to about 3 per cent'by moles of the silver halide in the'emulsion.

9. A photographic gelatino silver-halide emulsion containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced in the finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to from about 0.05 to about 3 per cent by moles, of the silver halide in the emulsion.

. 10. A photographic gel-atino silver halide emulsion containing a sensitizing dye for the emulsion, said dye being devoid of sulfonic, sulfinic, sulfuric and carboxylic acid groups and the metal and ammonium salt forms of said acid groups, and containing silver cyanide, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to from about 0.05 to about 3 per cent by moles of the silver halide in the emulsion;

1 1. A photographic gelatino silver halide emulsion selected from the group consisting of gelatino-silver-bromide and gelatino-silver-bromiodide emulsions containing a sensitizing dye for the emulsion, said dye being selected from the group consisting of cyanine, merocyanine, hemicyanine and hemioxonol dyes which are devoid of sulfonic, sulfinic, sulfuric and carboXylic acid groups and the metal and ammonium salt forms of said acid groups, and containing silver cyanide, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to from about 0.05 to about 3 per cent by moles of the silver'halide in the emulsion.

12. A photographic silver halide emulsion containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced in the finished emulsion in the form of the simple compound silver cyanide in a concentration of from about one-half to about two per cent by moles of the silver halide in the emulsion.

13. A photographic gelatino silver halide emulsion containing a sensitizing dye for the emulsion and containing silver cyanide, said silver cyanide having been introduced in the finished emulsion in the term of the simple compound silver cyanide in a concentration of from about one-half to about two per cent by moles of the silver halide in the emulsion.

14. A photographic gelatino silver halide emulsion containing a sensitizing dye for the emulsion, said dye being devoid of sulfonic, sulfinic, sulfuric and carboxylic acid groups and the metal and ammonium salt forms of said acid groups, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration of from about one-half to about two percent by moles of the silver halide in the emulsion.

15. A photographic gclatino silver halide emulsion selected from the group consisting of gelatino-silver-bromide and gel-atino-silver-bromiodide emulsions containing a sensitizing dye for the emulsion, said dye being selected from the group consisting of cyanine, merocyanine, hemicyanine, and hemioxonol dyes which are devoid of sulfonic, sulfinic, sulfuric and carbonylic acid groups and the metal and ammonium salt forms of said acid groups, and containing silver. cyanide, said silver cyanide having been introduced into the washed, finished emulsion in the form of the simple compound silver cyanide, in a concentration equal to from about one-half to about two per cent by moles of the silver halide in the emulsion.

JOHN A. LEERMAKERS. 25 

